Auto merge of #99047 - matthiaskrgr:rollup-01vn70s, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #95635 (sess: stabilize `--terminal-width` as `--diagnostic-width`)
 - #98718 (Stabilize `into_future`)
 - #98795 (A few cleanups)
 - #98798 (Fix caching bug in `download-rustc = true`)
 - #99019 (Add doc comments in `rustc_middle::mir`)
 - #99026 (Add test for and fix rust-lang/rust-clippy#9131)

Failed merges:

 - #98957 ( don't allow ZST in ScalarInt )

r? `@ghost`
`@rustbot` modify labels: rollup

52 files changed, 707 insertions, 665 deletions

diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs
index d0e0203bf8c..ea3602e8a05 100644
--- a/compiler/rustc_borrowck/src/region_infer/mod.rs
+++ b/compiler/rustc_borrowck/src/region_infer/mod.rs
@@ -495,8 +495,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     }
                 }
 
-                NllRegionVariableOrigin::RootEmptyRegion
-                | NllRegionVariableOrigin::Existential { .. } => {
+                NllRegionVariableOrigin::Existential { .. } => {
                     // For existential, regions, nothing to do.
                 }
             }
@@ -1410,8 +1409,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     self.check_bound_universal_region(fr, placeholder, errors_buffer);
                 }
 
-                NllRegionVariableOrigin::RootEmptyRegion
-                | NllRegionVariableOrigin::Existential { .. } => {
+                NllRegionVariableOrigin::Existential { .. } => {
                     // nothing to check here
                 }
             }
@@ -1513,8 +1511,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     self.check_bound_universal_region(fr, placeholder, errors_buffer);
                 }
 
-                NllRegionVariableOrigin::RootEmptyRegion
-                | NllRegionVariableOrigin::Existential { .. } => {
+                NllRegionVariableOrigin::Existential { .. } => {
                     // nothing to check here
                 }
             }
@@ -1788,9 +1785,9 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                 universe1.cannot_name(placeholder.universe)
             }
 
-            NllRegionVariableOrigin::RootEmptyRegion
-            | NllRegionVariableOrigin::FreeRegion
-            | NllRegionVariableOrigin::Existential { .. } => false,
+            NllRegionVariableOrigin::FreeRegion | NllRegionVariableOrigin::Existential { .. } => {
+                false
+            }
         }
     }
 
@@ -2152,8 +2149,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         let blame_source = match from_region_origin {
             NllRegionVariableOrigin::FreeRegion
             | NllRegionVariableOrigin::Existential { from_forall: false } => true,
-            NllRegionVariableOrigin::RootEmptyRegion
-            | NllRegionVariableOrigin::Placeholder(_)
+            NllRegionVariableOrigin::Placeholder(_)
             | NllRegionVariableOrigin::Existential { from_forall: true } => false,
         };
 
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index d129e845426..7c1fa28b8df 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -1,11 +1,20 @@
+use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::vec_map::VecMap;
 use rustc_hir::def_id::DefId;
 use rustc_hir::OpaqueTyOrigin;
+use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic;
 use rustc_infer::infer::InferCtxt;
+use rustc_infer::infer::TyCtxtInferExt as _;
+use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine};
+use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts};
+use rustc_middle::ty::visit::TypeVisitable;
 use rustc_middle::ty::{
-    self, OpaqueHiddenType, OpaqueTypeKey, TyCtxt, TypeFoldable, TypeVisitable,
+    self, OpaqueHiddenType, OpaqueTypeKey, ToPredicate, Ty, TyCtxt, TypeFoldable,
 };
-use rustc_trait_selection::opaque_types::InferCtxtExt;
+use rustc_span::Span;
+use rustc_trait_selection::traits::error_reporting::InferCtxtExt as _;
+use rustc_trait_selection::traits::TraitEngineExt as _;
 
 use super::RegionInferenceContext;
 
@@ -173,3 +182,474 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         })
     }
 }
+
+pub trait InferCtxtExt<'tcx> {
+    fn infer_opaque_definition_from_instantiation(
+        &self,
+        opaque_type_key: OpaqueTypeKey<'tcx>,
+        instantiated_ty: OpaqueHiddenType<'tcx>,
+        origin: OpaqueTyOrigin,
+    ) -> Ty<'tcx>;
+}
+
+impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
+    /// Given the fully resolved, instantiated type for an opaque
+    /// type, i.e., the value of an inference variable like C1 or C2
+    /// (*), computes the "definition type" for an opaque type
+    /// definition -- that is, the inferred value of `Foo1<'x>` or
+    /// `Foo2<'x>` that we would conceptually use in its definition:
+    /// ```ignore (illustrative)
+    /// type Foo1<'x> = impl Bar<'x> = AAA;  // <-- this type AAA
+    /// type Foo2<'x> = impl Bar<'x> = BBB;  // <-- or this type BBB
+    /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. }
+    /// ```
+    /// Note that these values are defined in terms of a distinct set of
+    /// generic parameters (`'x` instead of `'a`) from C1 or C2. The main
+    /// purpose of this function is to do that translation.
+    ///
+    /// (*) C1 and C2 were introduced in the comments on
+    /// `register_member_constraints`. Read that comment for more context.
+    ///
+    /// # Parameters
+    ///
+    /// - `def_id`, the `impl Trait` type
+    /// - `substs`, the substs  used to instantiate this opaque type
+    /// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of
+    ///   `opaque_defn.concrete_ty`
+    #[instrument(level = "debug", skip(self))]
+    fn infer_opaque_definition_from_instantiation(
+        &self,
+        opaque_type_key: OpaqueTypeKey<'tcx>,
+        instantiated_ty: OpaqueHiddenType<'tcx>,
+        origin: OpaqueTyOrigin,
+    ) -> Ty<'tcx> {
+        if self.is_tainted_by_errors() {
+            return self.tcx.ty_error();
+        }
+
+        let OpaqueTypeKey { def_id, substs } = opaque_type_key;
+
+        // Use substs to build up a reverse map from regions to their
+        // identity mappings. This is necessary because of `impl
+        // Trait` lifetimes are computed by replacing existing
+        // lifetimes with 'static and remapping only those used in the
+        // `impl Trait` return type, resulting in the parameters
+        // shifting.
+        let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id);
+        debug!(?id_substs);
+        let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> =
+            substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect();
+        debug!("map = {:#?}", map);
+
+        // Convert the type from the function into a type valid outside
+        // the function, by replacing invalid regions with 'static,
+        // after producing an error for each of them.
+        let definition_ty = instantiated_ty.ty.fold_with(&mut ReverseMapper::new(
+            self.tcx,
+            def_id,
+            map,
+            instantiated_ty.ty,
+            instantiated_ty.span,
+        ));
+        debug!(?definition_ty);
+
+        if !check_opaque_type_parameter_valid(
+            self.tcx,
+            opaque_type_key,
+            origin,
+            instantiated_ty.span,
+        ) {
+            return self.tcx.ty_error();
+        }
+
+        // Only check this for TAIT. RPIT already supports `src/test/ui/impl-trait/nested-return-type2.rs`
+        // on stable and we'd break that.
+        if let OpaqueTyOrigin::TyAlias = origin {
+            // This logic duplicates most of `check_opaque_meets_bounds`.
+            // FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely.
+            let param_env = self.tcx.param_env(def_id);
+            let body_id = self.tcx.local_def_id_to_hir_id(def_id.as_local().unwrap());
+            self.tcx.infer_ctxt().enter(move |infcx| {
+                // Require the hidden type to be well-formed with only the generics of the opaque type.
+                // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
+                // hidden type is well formed even without those bounds.
+                let predicate =
+                    ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into()))
+                        .to_predicate(infcx.tcx);
+                let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
+
+                // Require that the hidden type actually fulfills all the bounds of the opaque type, even without
+                // the bounds that the function supplies.
+                match infcx.register_hidden_type(
+                    OpaqueTypeKey { def_id, substs: id_substs },
+                    ObligationCause::misc(instantiated_ty.span, body_id),
+                    param_env,
+                    definition_ty,
+                    origin,
+                ) {
+                    Ok(infer_ok) => {
+                        for obligation in infer_ok.obligations {
+                            fulfillment_cx.register_predicate_obligation(&infcx, obligation);
+                        }
+                    }
+                    Err(err) => {
+                        infcx
+                            .report_mismatched_types(
+                                &ObligationCause::misc(instantiated_ty.span, body_id),
+                                self.tcx.mk_opaque(def_id, id_substs),
+                                definition_ty,
+                                err,
+                            )
+                            .emit();
+                    }
+                }
+
+                fulfillment_cx.register_predicate_obligation(
+                    &infcx,
+                    Obligation::misc(instantiated_ty.span, body_id, param_env, predicate),
+                );
+
+                // Check that all obligations are satisfied by the implementation's
+                // version.
+                let errors = fulfillment_cx.select_all_or_error(&infcx);
+
+                let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
+
+                if errors.is_empty() {
+                    definition_ty
+                } else {
+                    infcx.report_fulfillment_errors(&errors, None, false);
+                    self.tcx.ty_error()
+                }
+            })
+        } else {
+            definition_ty
+        }
+    }
+}
+
+fn check_opaque_type_parameter_valid(
+    tcx: TyCtxt<'_>,
+    opaque_type_key: OpaqueTypeKey<'_>,
+    origin: OpaqueTyOrigin,
+    span: Span,
+) -> bool {
+    match origin {
+        // No need to check return position impl trait (RPIT)
+        // because for type and const parameters they are correct
+        // by construction: we convert
+        //
+        // fn foo<P0..Pn>() -> impl Trait
+        //
+        // into
+        //
+        // type Foo<P0...Pn>
+        // fn foo<P0..Pn>() -> Foo<P0...Pn>.
+        //
+        // For lifetime parameters we convert
+        //
+        // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
+        //
+        // into
+        //
+        // type foo::<'p0..'pn>::Foo<'q0..'qm>
+        // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
+        //
+        // which would error here on all of the `'static` args.
+        OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true,
+        // Check these
+        OpaqueTyOrigin::TyAlias => {}
+    }
+    let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
+    let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
+    for (i, arg) in opaque_type_key.substs.iter().enumerate() {
+        let arg_is_param = match arg.unpack() {
+            GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
+            GenericArgKind::Lifetime(lt) if lt.is_static() => {
+                tcx.sess
+                    .struct_span_err(span, "non-defining opaque type use in defining scope")
+                    .span_label(
+                        tcx.def_span(opaque_generics.param_at(i, tcx).def_id),
+                        "cannot use static lifetime; use a bound lifetime \
+                                    instead or remove the lifetime parameter from the \
+                                    opaque type",
+                    )
+                    .emit();
+                return false;
+            }
+            GenericArgKind::Lifetime(lt) => {
+                matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_))
+            }
+            GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)),
+        };
+
+        if arg_is_param {
+            seen_params.entry(arg).or_default().push(i);
+        } else {
+            // Prevent `fn foo() -> Foo<u32>` from being defining.
+            let opaque_param = opaque_generics.param_at(i, tcx);
+            tcx.sess
+                .struct_span_err(span, "non-defining opaque type use in defining scope")
+                .span_note(
+                    tcx.def_span(opaque_param.def_id),
+                    &format!(
+                        "used non-generic {} `{}` for generic parameter",
+                        opaque_param.kind.descr(),
+                        arg,
+                    ),
+                )
+                .emit();
+            return false;
+        }
+    }
+
+    for (_, indices) in seen_params {
+        if indices.len() > 1 {
+            let descr = opaque_generics.param_at(indices[0], tcx).kind.descr();
+            let spans: Vec<_> = indices
+                .into_iter()
+                .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
+                .collect();
+            tcx.sess
+                .struct_span_err(span, "non-defining opaque type use in defining scope")
+                .span_note(spans, &format!("{} used multiple times", descr))
+                .emit();
+            return false;
+        }
+    }
+    true
+}
+
+struct ReverseMapper<'tcx> {
+    tcx: TyCtxt<'tcx>,
+
+    opaque_type_def_id: DefId,
+    map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
+    map_missing_regions_to_empty: bool,
+
+    /// initially `Some`, set to `None` once error has been reported
+    hidden_ty: Option<Ty<'tcx>>,
+
+    /// Span of function being checked.
+    span: Span,
+}
+
+impl<'tcx> ReverseMapper<'tcx> {
+    fn new(
+        tcx: TyCtxt<'tcx>,
+        opaque_type_def_id: DefId,
+        map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
+        hidden_ty: Ty<'tcx>,
+        span: Span,
+    ) -> Self {
+        Self {
+            tcx,
+            opaque_type_def_id,
+            map,
+            map_missing_regions_to_empty: false,
+            hidden_ty: Some(hidden_ty),
+            span,
+        }
+    }
+
+    fn fold_kind_mapping_missing_regions_to_empty(
+        &mut self,
+        kind: GenericArg<'tcx>,
+    ) -> GenericArg<'tcx> {
+        assert!(!self.map_missing_regions_to_empty);
+        self.map_missing_regions_to_empty = true;
+        let kind = kind.fold_with(self);
+        self.map_missing_regions_to_empty = false;
+        kind
+    }
+
+    fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> {
+        assert!(!self.map_missing_regions_to_empty);
+        kind.fold_with(self)
+    }
+}
+
+impl<'tcx> TypeFolder<'tcx> for ReverseMapper<'tcx> {
+    fn tcx(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+        match *r {
+            // Ignore bound regions and `'static` regions that appear in the
+            // type, we only need to remap regions that reference lifetimes
+            // from the function declaration.
+            // This would ignore `'r` in a type like `for<'r> fn(&'r u32)`.
+            ty::ReLateBound(..) | ty::ReStatic => return r,
+
+            // If regions have been erased (by writeback), don't try to unerase
+            // them.
+            ty::ReErased => return r,
+
+            // The regions that we expect from borrow checking.
+            ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReEmpty(ty::UniverseIndex::ROOT) => {}
+
+            ty::ReEmpty(_) | ty::RePlaceholder(_) | ty::ReVar(_) => {
+                // All of the regions in the type should either have been
+                // erased by writeback, or mapped back to named regions by
+                // borrow checking.
+                bug!("unexpected region kind in opaque type: {:?}", r);
+            }
+        }
+
+        let generics = self.tcx().generics_of(self.opaque_type_def_id);
+        match self.map.get(&r.into()).map(|k| k.unpack()) {
+            Some(GenericArgKind::Lifetime(r1)) => r1,
+            Some(u) => panic!("region mapped to unexpected kind: {:?}", u),
+            None if self.map_missing_regions_to_empty => self.tcx.lifetimes.re_root_empty,
+            None if generics.parent.is_some() => {
+                if let Some(hidden_ty) = self.hidden_ty.take() {
+                    unexpected_hidden_region_diagnostic(
+                        self.tcx,
+                        self.tcx.def_span(self.opaque_type_def_id),
+                        hidden_ty,
+                        r,
+                    )
+                    .emit();
+                }
+                self.tcx.lifetimes.re_root_empty
+            }
+            None => {
+                self.tcx
+                    .sess
+                    .struct_span_err(self.span, "non-defining opaque type use in defining scope")
+                    .span_label(
+                        self.span,
+                        format!(
+                            "lifetime `{}` is part of concrete type but not used in \
+                                 parameter list of the `impl Trait` type alias",
+                            r
+                        ),
+                    )
+                    .emit();
+
+                self.tcx().lifetimes.re_static
+            }
+        }
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        match *ty.kind() {
+            ty::Closure(def_id, substs) => {
+                // I am a horrible monster and I pray for death. When
+                // we encounter a closure here, it is always a closure
+                // from within the function that we are currently
+                // type-checking -- one that is now being encapsulated
+                // in an opaque type. Ideally, we would
+                // go through the types/lifetimes that it references
+                // and treat them just like we would any other type,
+                // which means we would error out if we find any
+                // reference to a type/region that is not in the
+                // "reverse map".
+                //
+                // **However,** in the case of closures, there is a
+                // somewhat subtle (read: hacky) consideration. The
+                // problem is that our closure types currently include
+                // all the lifetime parameters declared on the
+                // enclosing function, even if they are unused by the
+                // closure itself. We can't readily filter them out,
+                // so here we replace those values with `'empty`. This
+                // can't really make a difference to the rest of the
+                // compiler; those regions are ignored for the
+                // outlives relation, and hence don't affect trait
+                // selection or auto traits, and they are erased
+                // during codegen.
+
+                let generics = self.tcx.generics_of(def_id);
+                let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| {
+                    if index < generics.parent_count {
+                        // Accommodate missing regions in the parent kinds...
+                        self.fold_kind_mapping_missing_regions_to_empty(kind)
+                    } else {
+                        // ...but not elsewhere.
+                        self.fold_kind_normally(kind)
+                    }
+                }));
+
+                self.tcx.mk_closure(def_id, substs)
+            }
+
+            ty::Generator(def_id, substs, movability) => {
+                let generics = self.tcx.generics_of(def_id);
+                let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| {
+                    if index < generics.parent_count {
+                        // Accommodate missing regions in the parent kinds...
+                        self.fold_kind_mapping_missing_regions_to_empty(kind)
+                    } else {
+                        // ...but not elsewhere.
+                        self.fold_kind_normally(kind)
+                    }
+                }));
+
+                self.tcx.mk_generator(def_id, substs, movability)
+            }
+
+            ty::Param(param) => {
+                // Look it up in the substitution list.
+                match self.map.get(&ty.into()).map(|k| k.unpack()) {
+                    // Found it in the substitution list; replace with the parameter from the
+                    // opaque type.
+                    Some(GenericArgKind::Type(t1)) => t1,
+                    Some(u) => panic!("type mapped to unexpected kind: {:?}", u),
+                    None => {
+                        debug!(?param, ?self.map);
+                        self.tcx
+                            .sess
+                            .struct_span_err(
+                                self.span,
+                                &format!(
+                                    "type parameter `{}` is part of concrete type but not \
+                                          used in parameter list for the `impl Trait` type alias",
+                                    ty
+                                ),
+                            )
+                            .emit();
+
+                        self.tcx().ty_error()
+                    }
+                }
+            }
+
+            _ => ty.super_fold_with(self),
+        }
+    }
+
+    fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
+        trace!("checking const {:?}", ct);
+        // Find a const parameter
+        match ct.kind() {
+            ty::ConstKind::Param(..) => {
+                // Look it up in the substitution list.
+                match self.map.get(&ct.into()).map(|k| k.unpack()) {
+                    // Found it in the substitution list, replace with the parameter from the
+                    // opaque type.
+                    Some(GenericArgKind::Const(c1)) => c1,
+                    Some(u) => panic!("const mapped to unexpected kind: {:?}", u),
+                    None => {
+                        self.tcx
+                            .sess
+                            .struct_span_err(
+                                self.span,
+                                &format!(
+                                    "const parameter `{}` is part of concrete type but not \
+                                          used in parameter list for the `impl Trait` type alias",
+                                    ct
+                                ),
+                            )
+                            .emit();
+
+                        self.tcx().const_error(ct.ty())
+                    }
+                }
+            }
+
+            _ => ct,
+        }
+    }
+}
diff --git a/compiler/rustc_borrowck/src/universal_regions.rs b/compiler/rustc_borrowck/src/universal_regions.rs
index 89d84fcf09c..2a7713bc4df 100644
--- a/compiler/rustc_borrowck/src/universal_regions.rs
+++ b/compiler/rustc_borrowck/src/universal_regions.rs
@@ -503,7 +503,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
 
         let root_empty = self
             .infcx
-            .next_nll_region_var(NllRegionVariableOrigin::RootEmptyRegion)
+            .next_nll_region_var(NllRegionVariableOrigin::Existential { from_forall: true })
             .to_region_vid();
 
         UniversalRegions {
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 6d74e9a9f2b..85ea8eb3937 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -63,7 +63,7 @@ impl HumanReadableErrorType {
         bundle: Option<Lrc<FluentBundle>>,
         fallback_bundle: LazyFallbackBundle,
         teach: bool,
-        terminal_width: Option<usize>,
+        diagnostic_width: Option<usize>,
         macro_backtrace: bool,
     ) -> EmitterWriter {
         let (short, color_config) = self.unzip();
@@ -76,7 +76,7 @@ impl HumanReadableErrorType {
             short,
             teach,
             color,
-            terminal_width,
+            diagnostic_width,
             macro_backtrace,
         )
     }
@@ -710,7 +710,7 @@ pub struct EmitterWriter {
     short_message: bool,
     teach: bool,
     ui_testing: bool,
-    terminal_width: Option<usize>,
+    diagnostic_width: Option<usize>,
 
     macro_backtrace: bool,
 }
@@ -730,7 +730,7 @@ impl EmitterWriter {
         fallback_bundle: LazyFallbackBundle,
         short_message: bool,
         teach: bool,
-        terminal_width: Option<usize>,
+        diagnostic_width: Option<usize>,
         macro_backtrace: bool,
     ) -> EmitterWriter {
         let dst = Destination::from_stderr(color_config);
@@ -742,7 +742,7 @@ impl EmitterWriter {
             short_message,
             teach,
             ui_testing: false,
-            terminal_width,
+            diagnostic_width,
             macro_backtrace,
         }
     }
@@ -755,7 +755,7 @@ impl EmitterWriter {
         short_message: bool,
         teach: bool,
         colored: bool,
-        terminal_width: Option<usize>,
+        diagnostic_width: Option<usize>,
         macro_backtrace: bool,
     ) -> EmitterWriter {
         EmitterWriter {
@@ -766,7 +766,7 @@ impl EmitterWriter {
             short_message,
             teach,
             ui_testing: false,
-            terminal_width,
+            diagnostic_width,
             macro_backtrace,
         }
     }
@@ -1615,7 +1615,7 @@ impl EmitterWriter {
                     width_offset + annotated_file.multiline_depth + 1
                 };
 
-                let column_width = if let Some(width) = self.terminal_width {
+                let column_width = if let Some(width) = self.diagnostic_width {
                     width.saturating_sub(code_offset)
                 } else if self.ui_testing {
                     DEFAULT_COLUMN_WIDTH
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index d4d1491c169..b8cd334b4c6 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -42,7 +42,7 @@ pub struct JsonEmitter {
     pretty: bool,
     ui_testing: bool,
     json_rendered: HumanReadableErrorType,
-    terminal_width: Option<usize>,
+    diagnostic_width: Option<usize>,
     macro_backtrace: bool,
 }
 
@@ -54,7 +54,7 @@ impl JsonEmitter {
         fallback_bundle: LazyFallbackBundle,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
-        terminal_width: Option<usize>,
+        diagnostic_width: Option<usize>,
         macro_backtrace: bool,
     ) -> JsonEmitter {
         JsonEmitter {
@@ -66,7 +66,7 @@ impl JsonEmitter {
             pretty,
             ui_testing: false,
             json_rendered,
-            terminal_width,
+            diagnostic_width,
             macro_backtrace,
         }
     }
@@ -76,7 +76,7 @@ impl JsonEmitter {
         json_rendered: HumanReadableErrorType,
         fluent_bundle: Option<Lrc<FluentBundle>>,
         fallback_bundle: LazyFallbackBundle,
-        terminal_width: Option<usize>,
+        diagnostic_width: Option<usize>,
         macro_backtrace: bool,
     ) -> JsonEmitter {
         let file_path_mapping = FilePathMapping::empty();
@@ -87,7 +87,7 @@ impl JsonEmitter {
             fallback_bundle,
             pretty,
             json_rendered,
-            terminal_width,
+            diagnostic_width,
             macro_backtrace,
         )
     }
@@ -100,7 +100,7 @@ impl JsonEmitter {
         fallback_bundle: LazyFallbackBundle,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
-        terminal_width: Option<usize>,
+        diagnostic_width: Option<usize>,
         macro_backtrace: bool,
     ) -> JsonEmitter {
         JsonEmitter {
@@ -112,7 +112,7 @@ impl JsonEmitter {
             pretty,
             ui_testing: false,
             json_rendered,
-            terminal_width,
+            diagnostic_width,
             macro_backtrace,
         }
     }
@@ -345,7 +345,7 @@ impl Diagnostic {
                 je.fluent_bundle.clone(),
                 je.fallback_bundle.clone(),
                 false,
-                je.terminal_width,
+                je.diagnostic_width,
                 je.macro_backtrace,
             )
             .ui_testing(je.ui_testing)
diff --git a/compiler/rustc_infer/src/infer/free_regions.rs b/compiler/rustc_infer/src/infer/free_regions.rs
index fad949a3bc6..d566634a492 100644
--- a/compiler/rustc_infer/src/infer/free_regions.rs
+++ b/compiler/rustc_infer/src/infer/free_regions.rs
@@ -4,7 +4,7 @@
 //! and use that to decide when one free region outlives another, and so forth.
 
 use rustc_data_structures::transitive_relation::TransitiveRelation;
-use rustc_middle::ty::{self, Lift, Region, TyCtxt};
+use rustc_middle::ty::{Lift, Region, TyCtxt};
 
 /// Combines a `FreeRegionMap` and a `TyCtxt`.
 ///
@@ -49,7 +49,7 @@ impl<'tcx> FreeRegionMap<'tcx> {
     // (with the exception that `'static: 'x` is not notable)
     pub fn relate_regions(&mut self, sub: Region<'tcx>, sup: Region<'tcx>) {
         debug!("relate_regions(sub={:?}, sup={:?})", sub, sup);
-        if self.is_free_or_static(sub) && self.is_free(sup) {
+        if sub.is_free_or_static() && sup.is_free() {
             self.relation.add(sub, sup)
         }
     }
@@ -68,7 +68,7 @@ impl<'tcx> FreeRegionMap<'tcx> {
         r_a: Region<'tcx>,
         r_b: Region<'tcx>,
     ) -> bool {
-        assert!(self.is_free_or_static(r_a) && self.is_free_or_static(r_b));
+        assert!(r_a.is_free_or_static() && r_b.is_free_or_static());
         let re_static = tcx.lifetimes.re_static;
         if self.check_relation(re_static, r_b) {
             // `'a <= 'static` is always true, and not stored in the
@@ -85,20 +85,6 @@ impl<'tcx> FreeRegionMap<'tcx> {
         r_a == r_b || self.relation.contains(r_a, r_b)
     }
 
-    /// True for free regions other than `'static`.
-    pub fn is_free(&self, r: Region<'_>) -> bool {
-        matches!(*r, ty::ReEarlyBound(_) | ty::ReFree(_))
-    }
-
-    /// True if `r` is a free region or static of the sort that this
-    /// free region map can be used with.
-    pub fn is_free_or_static(&self, r: Region<'_>) -> bool {
-        match *r {
-            ty::ReStatic => true,
-            _ => self.is_free(r),
-        }
-    }
-
     /// Computes the least-upper-bound of two free regions. In some
     /// cases, this is more conservative than necessary, in order to
     /// avoid making arbitrary choices. See
@@ -110,8 +96,8 @@ impl<'tcx> FreeRegionMap<'tcx> {
         r_b: Region<'tcx>,
     ) -> Region<'tcx> {
         debug!("lub_free_regions(r_a={:?}, r_b={:?})", r_a, r_b);
-        assert!(self.is_free(r_a));
-        assert!(self.is_free(r_b));
+        assert!(r_a.is_free());
+        assert!(r_b.is_free());
         let result = if r_a == r_b {
             r_a
         } else {
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
index 87fa22b3835..3783cfb4cc5 100644
--- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
+++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -47,7 +47,6 @@ pub(crate) fn resolve<'tcx>(
 #[derive(Clone)]
 pub struct LexicalRegionResolutions<'tcx> {
     pub(crate) values: IndexVec<RegionVid, VarValue<'tcx>>,
-    pub(crate) error_region: ty::Region<'tcx>,
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -140,7 +139,6 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
     /// empty region. The `expansion` phase will grow this larger.
     fn construct_var_data(&self, tcx: TyCtxt<'tcx>) -> LexicalRegionResolutions<'tcx> {
         LexicalRegionResolutions {
-            error_region: tcx.lifetimes.re_static,
             values: IndexVec::from_fn_n(
                 |vid| {
                     let vid_universe = self.var_infos[vid].universe;
@@ -310,7 +308,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
 
         // Check for the case where we know that `'b: 'static` -- in that case,
         // `a <= b` for all `a`.
-        let b_free_or_static = self.region_rels.free_regions.is_free_or_static(b);
+        let b_free_or_static = b.is_free_or_static();
         if b_free_or_static && sub_free_regions(tcx.lifetimes.re_static, b) {
             return true;
         }
@@ -320,7 +318,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
         // `lub` relationship defined below, since sometimes the "lub"
         // is actually the `postdom_upper_bound` (see
         // `TransitiveRelation` for more details).
-        let a_free_or_static = self.region_rels.free_regions.is_free_or_static(a);
+        let a_free_or_static = a.is_free_or_static();
         if a_free_or_static && b_free_or_static {
             return sub_free_regions(a, b);
         }
@@ -864,10 +862,7 @@ impl<'tcx> LexicalRegionResolutions<'tcx> {
     where
         T: TypeFoldable<'tcx>,
     {
-        tcx.fold_regions(value, |r, _db| match *r {
-            ty::ReVar(rid) => self.resolve_var(rid),
-            _ => r,
-        })
+        tcx.fold_regions(value, |r, _db| self.resolve_region(tcx, r))
     }
 
     fn value(&self, rid: RegionVid) -> &VarValue<'tcx> {
@@ -878,12 +873,19 @@ impl<'tcx> LexicalRegionResolutions<'tcx> {
         &mut self.values[rid]
     }
 
-    pub fn resolve_var(&self, rid: RegionVid) -> ty::Region<'tcx> {
-        let result = match self.values[rid] {
-            VarValue::Value(r) => r,
-            VarValue::ErrorValue => self.error_region,
+    pub(crate) fn resolve_region(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        r: ty::Region<'tcx>,
+    ) -> ty::Region<'tcx> {
+        let result = match *r {
+            ty::ReVar(rid) => match self.values[rid] {
+                VarValue::Value(r) => r,
+                VarValue::ErrorValue => tcx.lifetimes.re_static,
+            },
+            _ => r,
         };
-        debug!("resolve_var({:?}) = {:?}", rid, result);
+        debug!("resolve_region({:?}) = {:?}", r, result);
         result
     }
 }
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 991fd23ab43..6e0f2d68743 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -466,9 +466,6 @@ pub enum NllRegionVariableOrigin {
     /// from a `for<'a> T` binder). Meant to represent "any region".
     Placeholder(ty::PlaceholderRegion),
 
-    /// The variable we create to represent `'empty(U0)`.
-    RootEmptyRegion,
-
     Existential {
         /// If this is true, then this variable was created to represent a lifetime
         /// bound in a `for` binder. For example, it might have been created to
@@ -1250,7 +1247,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         };
 
         let lexical_region_resolutions = LexicalRegionResolutions {
-            error_region: self.tcx.lifetimes.re_static,
             values: rustc_index::vec::IndexVec::from_elem_n(
                 crate::infer::lexical_region_resolve::VarValue::Value(self.tcx.lifetimes.re_erased),
                 var_infos.len(),
diff --git a/compiler/rustc_infer/src/infer/resolve.rs b/compiler/rustc_infer/src/infer/resolve.rs
index a6145687429..3d99f0958f7 100644
--- a/compiler/rustc_infer/src/infer/resolve.rs
+++ b/compiler/rustc_infer/src/infer/resolve.rs
@@ -206,13 +206,13 @@ impl<'a, 'tcx> FallibleTypeFolder<'tcx> for FullTypeResolver<'a, 'tcx> {
 
     fn try_fold_region(&mut self, r: ty::Region<'tcx>) -> Result<ty::Region<'tcx>, Self::Error> {
         match *r {
-            ty::ReVar(rid) => Ok(self
+            ty::ReVar(_) => Ok(self
                 .infcx
                 .lexical_region_resolutions
                 .borrow()
                 .as_ref()
                 .expect("region resolution not performed")
-                .resolve_var(rid)),
+                .resolve_region(self.infcx.tcx, r)),
             _ => Ok(r),
         }
     }
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 30a29ed6ed3..81145416437 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -689,7 +689,6 @@ fn test_debugging_options_tracking_hash() {
     untracked!(span_debug, true);
     untracked!(span_free_formats, true);
     untracked!(temps_dir, Some(String::from("abc")));
-    untracked!(terminal_width, Some(80));
     untracked!(threads, 99);
     untracked!(time, true);
     untracked!(time_llvm_passes, true);
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 93686128101..f136b8e2368 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1048,6 +1048,8 @@ impl BasicBlock {
 ///////////////////////////////////////////////////////////////////////////
 // BasicBlockData
 
+/// Data for a basic block, including a list of its statements.
+///
 /// See [`BasicBlock`] for documentation on what basic blocks are at a high level.
 #[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
 pub struct BasicBlockData<'tcx> {
@@ -1079,7 +1081,7 @@ impl<'tcx> BasicBlockData<'tcx> {
     /// Accessor for terminator.
     ///
     /// Terminator may not be None after construction of the basic block is complete. This accessor
-    /// provides a convenience way to reach the terminator.
+    /// provides a convenient way to reach the terminator.
     #[inline]
     pub fn terminator(&self) -> &Terminator<'tcx> {
         self.terminator.as_ref().expect("invalid terminator state")
@@ -1286,6 +1288,7 @@ impl<O: fmt::Debug> fmt::Debug for AssertKind<O> {
 ///////////////////////////////////////////////////////////////////////////
 // Statements
 
+/// A statement in a basic block, including information about its source code.
 #[derive(Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
 pub struct Statement<'tcx> {
     pub source_info: SourceInfo,
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 815e39aab57..03e4319bbf1 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1570,6 +1570,19 @@ impl<'tcx> Region<'tcx> {
             _ => bug!("free_region_binding_scope invoked on inappropriate region: {:?}", self),
         }
     }
+
+    /// True for free regions other than `'static`.
+    pub fn is_free(self) -> bool {
+        matches!(*self, ty::ReEarlyBound(_) | ty::ReFree(_))
+    }
+
+    /// True if `self` is a free region or static.
+    pub fn is_free_or_static(self) -> bool {
+        match *self {
+            ty::ReStatic => true,
+            _ => self.is_free(),
+        }
+    }
 }
 
 /// Type utilities
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index e7717f1367c..b7da0f22942 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -726,6 +726,7 @@ impl Default for Options {
             prints: Vec::new(),
             cg: Default::default(),
             error_format: ErrorOutputType::default(),
+            diagnostic_width: None,
             externs: Externs(BTreeMap::new()),
             crate_name: None,
             libs: Vec::new(),
@@ -1427,6 +1428,12 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
                                  never  = never colorize output",
             "auto|always|never",
         ),
+        opt::opt_s(
+            "",
+            "diagnostic-width",
+            "Inform rustc of the width of the output so that diagnostics can be truncated to fit",
+            "WIDTH",
+        ),
         opt::multi_s(
             "",
             "remap-path-prefix",
@@ -2202,6 +2209,10 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
 
     let error_format = parse_error_format(matches, color, json_rendered);
 
+    let diagnostic_width = matches.opt_get("diagnostic-width").unwrap_or_else(|_| {
+        early_error(error_format, "`--diagnostic-width` must be an positive integer");
+    });
+
     let unparsed_crate_types = matches.opt_strs("crate-type");
     let crate_types = parse_crate_types_from_list(unparsed_crate_types)
         .unwrap_or_else(|e| early_error(error_format, &e));
@@ -2474,6 +2485,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         prints,
         cg,
         error_format,
+        diagnostic_width,
         externs,
         unstable_features: UnstableFeatures::from_environment(crate_name.as_deref()),
         crate_name,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index be70ea5d5e4..b0c74ffb6dc 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -170,6 +170,7 @@ top_level_options!(
 
         test: bool [TRACKED],
         error_format: ErrorOutputType [UNTRACKED],
+        diagnostic_width: Option<usize> [UNTRACKED],
 
         /// If `Some`, enable incremental compilation, using the given
         /// directory to store intermediate results.
@@ -1388,6 +1389,8 @@ options! {
         "panic strategy for out-of-memory handling"),
     osx_rpath_install_name: bool = (false, parse_bool, [TRACKED],
         "pass `-install_name @rpath/...` to the macOS linker (default: no)"),
+    diagnostic_width: Option<usize> = (None, parse_opt_number, [UNTRACKED],
+        "set the current output width for diagnostic truncation"),
     panic_abort_tests: bool = (false, parse_bool, [TRACKED],
         "support compiling tests with panic=abort (default: no)"),
     panic_in_drop: PanicStrategy = (PanicStrategy::Unwind, parse_panic_strategy, [TRACKED],
@@ -1514,8 +1517,6 @@ options! {
         "show extended diagnostic help (default: no)"),
     temps_dir: Option<String> = (None, parse_opt_string, [UNTRACKED],
         "the directory the intermediate files are written to"),
-    terminal_width: Option<usize> = (None, parse_opt_number, [UNTRACKED],
-        "set the current terminal width"),
     // Diagnostics are considered side-effects of a query (see `QuerySideEffects`) and are saved
     // alongside query results and changes to translation options can affect diagnostics - so
     // translation options should be tracked.
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 2a5ddd4e9e4..52b9ee94718 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1162,7 +1162,7 @@ fn default_emitter(
                         fallback_bundle,
                         short,
                         sopts.debugging_opts.teach,
-                        sopts.debugging_opts.terminal_width,
+                        sopts.diagnostic_width,
                         macro_backtrace,
                     ),
                     Some(dst) => EmitterWriter::new(
@@ -1173,7 +1173,7 @@ fn default_emitter(
                         short,
                         false, // no teach messages when writing to a buffer
                         false, // no colors when writing to a buffer
-                        None,  // no terminal width
+                        None,  // no diagnostic width
                         macro_backtrace,
                     ),
                 };
@@ -1188,7 +1188,7 @@ fn default_emitter(
                 fallback_bundle,
                 pretty,
                 json_rendered,
-                sopts.debugging_opts.terminal_width,
+                sopts.diagnostic_width,
                 macro_backtrace,
             )
             .ui_testing(sopts.debugging_opts.ui_testing),
@@ -1202,7 +1202,7 @@ fn default_emitter(
                 fallback_bundle,
                 pretty,
                 json_rendered,
-                sopts.debugging_opts.terminal_width,
+                sopts.diagnostic_width,
                 macro_backtrace,
             )
             .ui_testing(sopts.debugging_opts.ui_testing),
diff --git a/compiler/rustc_trait_selection/src/lib.rs b/compiler/rustc_trait_selection/src/lib.rs
index 44ff3fd7306..282ee632ce5 100644
--- a/compiler/rustc_trait_selection/src/lib.rs
+++ b/compiler/rustc_trait_selection/src/lib.rs
@@ -37,5 +37,4 @@ extern crate smallvec;
 
 pub mod autoderef;
 pub mod infer;
-pub mod opaque_types;
 pub mod traits;
diff --git a/compiler/rustc_trait_selection/src/opaque_types.rs b/compiler/rustc_trait_selection/src/opaque_types.rs
deleted file mode 100644
index d290f7b074c..00000000000
--- a/compiler/rustc_trait_selection/src/opaque_types.rs
+++ /dev/null
@@ -1,545 +0,0 @@
-use crate::traits;
-use crate::traits::error_reporting::InferCtxtExt as _;
-use crate::traits::TraitEngineExt as _;
-use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::def_id::DefId;
-use rustc_hir::OpaqueTyOrigin;
-use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic;
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt as _};
-use rustc_infer::traits::{Obligation, ObligationCause, TraitEngine};
-use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
-use rustc_middle::ty::subst::{GenericArg, GenericArgKind, InternalSubsts};
-use rustc_middle::ty::visit::TypeVisitable;
-use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey, ToPredicate, Ty, TyCtxt};
-use rustc_span::Span;
-
-pub trait InferCtxtExt<'tcx> {
-    fn infer_opaque_definition_from_instantiation(
-        &self,
-        opaque_type_key: OpaqueTypeKey<'tcx>,
-        instantiated_ty: OpaqueHiddenType<'tcx>,
-        origin: OpaqueTyOrigin,
-    ) -> Ty<'tcx>;
-}
-
-impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
-    /// Given the fully resolved, instantiated type for an opaque
-    /// type, i.e., the value of an inference variable like C1 or C2
-    /// (*), computes the "definition type" for an opaque type
-    /// definition -- that is, the inferred value of `Foo1<'x>` or
-    /// `Foo2<'x>` that we would conceptually use in its definition:
-    /// ```ignore (illustrative)
-    /// type Foo1<'x> = impl Bar<'x> = AAA;  // <-- this type AAA
-    /// type Foo2<'x> = impl Bar<'x> = BBB;  // <-- or this type BBB
-    /// fn foo<'a, 'b>(..) -> (Foo1<'a>, Foo2<'b>) { .. }
-    /// ```
-    /// Note that these values are defined in terms of a distinct set of
-    /// generic parameters (`'x` instead of `'a`) from C1 or C2. The main
-    /// purpose of this function is to do that translation.
-    ///
-    /// (*) C1 and C2 were introduced in the comments on
-    /// `register_member_constraints`. Read that comment for more context.
-    ///
-    /// # Parameters
-    ///
-    /// - `def_id`, the `impl Trait` type
-    /// - `substs`, the substs  used to instantiate this opaque type
-    /// - `instantiated_ty`, the inferred type C1 -- fully resolved, lifted version of
-    ///   `opaque_defn.concrete_ty`
-    #[instrument(level = "debug", skip(self))]
-    fn infer_opaque_definition_from_instantiation(
-        &self,
-        opaque_type_key: OpaqueTypeKey<'tcx>,
-        instantiated_ty: OpaqueHiddenType<'tcx>,
-        origin: OpaqueTyOrigin,
-    ) -> Ty<'tcx> {
-        if self.is_tainted_by_errors() {
-            return self.tcx.ty_error();
-        }
-
-        let OpaqueTypeKey { def_id, substs } = opaque_type_key;
-
-        // Use substs to build up a reverse map from regions to their
-        // identity mappings. This is necessary because of `impl
-        // Trait` lifetimes are computed by replacing existing
-        // lifetimes with 'static and remapping only those used in the
-        // `impl Trait` return type, resulting in the parameters
-        // shifting.
-        let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id);
-        debug!(?id_substs);
-        let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> =
-            substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect();
-        debug!("map = {:#?}", map);
-
-        // Convert the type from the function into a type valid outside
-        // the function, by replacing invalid regions with 'static,
-        // after producing an error for each of them.
-        let definition_ty = instantiated_ty.ty.fold_with(&mut ReverseMapper::new(
-            self.tcx,
-            def_id,
-            map,
-            instantiated_ty.ty,
-            instantiated_ty.span,
-        ));
-        debug!(?definition_ty);
-
-        if !check_opaque_type_parameter_valid(
-            self.tcx,
-            opaque_type_key,
-            origin,
-            instantiated_ty.span,
-        ) {
-            return self.tcx.ty_error();
-        }
-
-        // Only check this for TAIT. RPIT already supports `src/test/ui/impl-trait/nested-return-type2.rs`
-        // on stable and we'd break that.
-        if let OpaqueTyOrigin::TyAlias = origin {
-            // This logic duplicates most of `check_opaque_meets_bounds`.
-            // FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely.
-            let param_env = self.tcx.param_env(def_id);
-            let body_id = self.tcx.local_def_id_to_hir_id(def_id.as_local().unwrap());
-            self.tcx.infer_ctxt().enter(move |infcx| {
-                // Require the hidden type to be well-formed with only the generics of the opaque type.
-                // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
-                // hidden type is well formed even without those bounds.
-                let predicate =
-                    ty::Binder::dummy(ty::PredicateKind::WellFormed(definition_ty.into()))
-                        .to_predicate(infcx.tcx);
-                let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
-
-                // Require that the hidden type actually fulfills all the bounds of the opaque type, even without
-                // the bounds that the function supplies.
-                match infcx.register_hidden_type(
-                    OpaqueTypeKey { def_id, substs: id_substs },
-                    ObligationCause::misc(instantiated_ty.span, body_id),
-                    param_env,
-                    definition_ty,
-                    origin,
-                ) {
-                    Ok(infer_ok) => {
-                        for obligation in infer_ok.obligations {
-                            fulfillment_cx.register_predicate_obligation(&infcx, obligation);
-                        }
-                    }
-                    Err(err) => {
-                        infcx
-                            .report_mismatched_types(
-                                &ObligationCause::misc(instantiated_ty.span, body_id),
-                                self.tcx.mk_opaque(def_id, id_substs),
-                                definition_ty,
-                                err,
-                            )
-                            .emit();
-                    }
-                }
-
-                fulfillment_cx.register_predicate_obligation(
-                    &infcx,
-                    Obligation::misc(instantiated_ty.span, body_id, param_env, predicate),
-                );
-
-                // Check that all obligations are satisfied by the implementation's
-                // version.
-                let errors = fulfillment_cx.select_all_or_error(&infcx);
-
-                let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
-
-                if errors.is_empty() {
-                    definition_ty
-                } else {
-                    infcx.report_fulfillment_errors(&errors, None, false);
-                    self.tcx.ty_error()
-                }
-            })
-        } else {
-            definition_ty
-        }
-    }
-}
-
-fn check_opaque_type_parameter_valid(
-    tcx: TyCtxt<'_>,
-    opaque_type_key: OpaqueTypeKey<'_>,
-    origin: OpaqueTyOrigin,
-    span: Span,
-) -> bool {
-    match origin {
-        // No need to check return position impl trait (RPIT)
-        // because for type and const parameters they are correct
-        // by construction: we convert
-        //
-        // fn foo<P0..Pn>() -> impl Trait
-        //
-        // into
-        //
-        // type Foo<P0...Pn>
-        // fn foo<P0..Pn>() -> Foo<P0...Pn>.
-        //
-        // For lifetime parameters we convert
-        //
-        // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
-        //
-        // into
-        //
-        // type foo::<'p0..'pn>::Foo<'q0..'qm>
-        // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
-        //
-        // which would error here on all of the `'static` args.
-        OpaqueTyOrigin::FnReturn(..) | OpaqueTyOrigin::AsyncFn(..) => return true,
-        // Check these
-        OpaqueTyOrigin::TyAlias => {}
-    }
-    let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
-    let mut seen_params: FxHashMap<_, Vec<_>> = FxHashMap::default();
-    for (i, arg) in opaque_type_key.substs.iter().enumerate() {
-        let arg_is_param = match arg.unpack() {
-            GenericArgKind::Type(ty) => matches!(ty.kind(), ty::Param(_)),
-            GenericArgKind::Lifetime(lt) if lt.is_static() => {
-                tcx.sess
-                    .struct_span_err(span, "non-defining opaque type use in defining scope")
-                    .span_label(
-                        tcx.def_span(opaque_generics.param_at(i, tcx).def_id),
-                        "cannot use static lifetime; use a bound lifetime \
-                                    instead or remove the lifetime parameter from the \
-                                    opaque type",
-                    )
-                    .emit();
-                return false;
-            }
-            GenericArgKind::Lifetime(lt) => {
-                matches!(*lt, ty::ReEarlyBound(_) | ty::ReFree(_))
-            }
-            GenericArgKind::Const(ct) => matches!(ct.kind(), ty::ConstKind::Param(_)),
-        };
-
-        if arg_is_param {
-            seen_params.entry(arg).or_default().push(i);
-        } else {
-            // Prevent `fn foo() -> Foo<u32>` from being defining.
-            let opaque_param = opaque_generics.param_at(i, tcx);
-            tcx.sess
-                .struct_span_err(span, "non-defining opaque type use in defining scope")
-                .span_note(
-                    tcx.def_span(opaque_param.def_id),
-                    &format!(
-                        "used non-generic {} `{}` for generic parameter",
-                        opaque_param.kind.descr(),
-                        arg,
-                    ),
-                )
-                .emit();
-            return false;
-        }
-    }
-
-    for (_, indices) in seen_params {
-        if indices.len() > 1 {
-            let descr = opaque_generics.param_at(indices[0], tcx).kind.descr();
-            let spans: Vec<_> = indices
-                .into_iter()
-                .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
-                .collect();
-            tcx.sess
-                .struct_span_err(span, "non-defining opaque type use in defining scope")
-                .span_note(spans, &format!("{} used multiple times", descr))
-                .emit();
-            return false;
-        }
-    }
-    true
-}
-
-struct ReverseMapper<'tcx> {
-    tcx: TyCtxt<'tcx>,
-
-    opaque_type_def_id: DefId,
-    map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
-    map_missing_regions_to_empty: bool,
-
-    /// initially `Some`, set to `None` once error has been reported
-    hidden_ty: Option<Ty<'tcx>>,
-
-    /// Span of function being checked.
-    span: Span,
-}
-
-impl<'tcx> ReverseMapper<'tcx> {
-    fn new(
-        tcx: TyCtxt<'tcx>,
-        opaque_type_def_id: DefId,
-        map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
-        hidden_ty: Ty<'tcx>,
-        span: Span,
-    ) -> Self {
-        Self {
-            tcx,
-            opaque_type_def_id,
-            map,
-            map_missing_regions_to_empty: false,
-            hidden_ty: Some(hidden_ty),
-            span,
-        }
-    }
-
-    fn fold_kind_mapping_missing_regions_to_empty(
-        &mut self,
-        kind: GenericArg<'tcx>,
-    ) -> GenericArg<'tcx> {
-        assert!(!self.map_missing_regions_to_empty);
-        self.map_missing_regions_to_empty = true;
-        let kind = kind.fold_with(self);
-        self.map_missing_regions_to_empty = false;
-        kind
-    }
-
-    fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> {
-        assert!(!self.map_missing_regions_to_empty);
-        kind.fold_with(self)
-    }
-}
-
-impl<'tcx> TypeFolder<'tcx> for ReverseMapper<'tcx> {
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-
-    #[instrument(skip(self), level = "debug")]
-    fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
-        match *r {
-            // Ignore bound regions and `'static` regions that appear in the
-            // type, we only need to remap regions that reference lifetimes
-            // from the function declaration.
-            // This would ignore `'r` in a type like `for<'r> fn(&'r u32)`.
-            ty::ReLateBound(..) | ty::ReStatic => return r,
-
-            // If regions have been erased (by writeback), don't try to unerase
-            // them.
-            ty::ReErased => return r,
-
-            // The regions that we expect from borrow checking.
-            ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReEmpty(ty::UniverseIndex::ROOT) => {}
-
-            ty::ReEmpty(_) | ty::RePlaceholder(_) | ty::ReVar(_) => {
-                // All of the regions in the type should either have been
-                // erased by writeback, or mapped back to named regions by
-                // borrow checking.
-                bug!("unexpected region kind in opaque type: {:?}", r);
-            }
-        }
-
-        let generics = self.tcx().generics_of(self.opaque_type_def_id);
-        match self.map.get(&r.into()).map(|k| k.unpack()) {
-            Some(GenericArgKind::Lifetime(r1)) => r1,
-            Some(u) => panic!("region mapped to unexpected kind: {:?}", u),
-            None if self.map_missing_regions_to_empty => self.tcx.lifetimes.re_root_empty,
-            None if generics.parent.is_some() => {
-                if let Some(hidden_ty) = self.hidden_ty.take() {
-                    unexpected_hidden_region_diagnostic(
-                        self.tcx,
-                        self.tcx.def_span(self.opaque_type_def_id),
-                        hidden_ty,
-                        r,
-                    )
-                    .emit();
-                }
-                self.tcx.lifetimes.re_root_empty
-            }
-            None => {
-                self.tcx
-                    .sess
-                    .struct_span_err(self.span, "non-defining opaque type use in defining scope")
-                    .span_label(
-                        self.span,
-                        format!(
-                            "lifetime `{}` is part of concrete type but not used in \
-                                 parameter list of the `impl Trait` type alias",
-                            r
-                        ),
-                    )
-                    .emit();
-
-                self.tcx().lifetimes.re_static
-            }
-        }
-    }
-
-    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        match *ty.kind() {
-            ty::Closure(def_id, substs) => {
-                // I am a horrible monster and I pray for death. When
-                // we encounter a closure here, it is always a closure
-                // from within the function that we are currently
-                // type-checking -- one that is now being encapsulated
-                // in an opaque type. Ideally, we would
-                // go through the types/lifetimes that it references
-                // and treat them just like we would any other type,
-                // which means we would error out if we find any
-                // reference to a type/region that is not in the
-                // "reverse map".
-                //
-                // **However,** in the case of closures, there is a
-                // somewhat subtle (read: hacky) consideration. The
-                // problem is that our closure types currently include
-                // all the lifetime parameters declared on the
-                // enclosing function, even if they are unused by the
-                // closure itself. We can't readily filter them out,
-                // so here we replace those values with `'empty`. This
-                // can't really make a difference to the rest of the
-                // compiler; those regions are ignored for the
-                // outlives relation, and hence don't affect trait
-                // selection or auto traits, and they are erased
-                // during codegen.
-
-                let generics = self.tcx.generics_of(def_id);
-                let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| {
-                    if index < generics.parent_count {
-                        // Accommodate missing regions in the parent kinds...
-                        self.fold_kind_mapping_missing_regions_to_empty(kind)
-                    } else {
-                        // ...but not elsewhere.
-                        self.fold_kind_normally(kind)
-                    }
-                }));
-
-                self.tcx.mk_closure(def_id, substs)
-            }
-
-            ty::Generator(def_id, substs, movability) => {
-                let generics = self.tcx.generics_of(def_id);
-                let substs = self.tcx.mk_substs(substs.iter().enumerate().map(|(index, kind)| {
-                    if index < generics.parent_count {
-                        // Accommodate missing regions in the parent kinds...
-                        self.fold_kind_mapping_missing_regions_to_empty(kind)
-                    } else {
-                        // ...but not elsewhere.
-                        self.fold_kind_normally(kind)
-                    }
-                }));
-
-                self.tcx.mk_generator(def_id, substs, movability)
-            }
-
-            ty::Param(param) => {
-                // Look it up in the substitution list.
-                match self.map.get(&ty.into()).map(|k| k.unpack()) {
-                    // Found it in the substitution list; replace with the parameter from the
-                    // opaque type.
-                    Some(GenericArgKind::Type(t1)) => t1,
-                    Some(u) => panic!("type mapped to unexpected kind: {:?}", u),
-                    None => {
-                        debug!(?param, ?self.map);
-                        self.tcx
-                            .sess
-                            .struct_span_err(
-                                self.span,
-                                &format!(
-                                    "type parameter `{}` is part of concrete type but not \
-                                          used in parameter list for the `impl Trait` type alias",
-                                    ty
-                                ),
-                            )
-                            .emit();
-
-                        self.tcx().ty_error()
-                    }
-                }
-            }
-
-            _ => ty.super_fold_with(self),
-        }
-    }
-
-    fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
-        trace!("checking const {:?}", ct);
-        // Find a const parameter
-        match ct.kind() {
-            ty::ConstKind::Param(..) => {
-                // Look it up in the substitution list.
-                match self.map.get(&ct.into()).map(|k| k.unpack()) {
-                    // Found it in the substitution list, replace with the parameter from the
-                    // opaque type.
-                    Some(GenericArgKind::Const(c1)) => c1,
-                    Some(u) => panic!("const mapped to unexpected kind: {:?}", u),
-                    None => {
-                        self.tcx
-                            .sess
-                            .struct_span_err(
-                                self.span,
-                                &format!(
-                                    "const parameter `{}` is part of concrete type but not \
-                                          used in parameter list for the `impl Trait` type alias",
-                                    ct
-                                ),
-                            )
-                            .emit();
-
-                        self.tcx().const_error(ct.ty())
-                    }
-                }
-            }
-
-            _ => ct,
-        }
-    }
-}
-
-/// Given a set of predicates that apply to an object type, returns
-/// the region bounds that the (erased) `Self` type must
-/// outlive. Precisely *because* the `Self` type is erased, the
-/// parameter `erased_self_ty` must be supplied to indicate what type
-/// has been used to represent `Self` in the predicates
-/// themselves. This should really be a unique type; `FreshTy(0)` is a
-/// popular choice.
-///
-/// N.B., in some cases, particularly around higher-ranked bounds,
-/// this function returns a kind of conservative approximation.
-/// That is, all regions returned by this function are definitely
-/// required, but there may be other region bounds that are not
-/// returned, as well as requirements like `for<'a> T: 'a`.
-///
-/// Requires that trait definitions have been processed so that we can
-/// elaborate predicates and walk supertraits.
-#[instrument(skip(tcx, predicates), level = "debug")]
-pub(crate) fn required_region_bounds<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    erased_self_ty: Ty<'tcx>,
-    predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
-) -> Vec<ty::Region<'tcx>> {
-    assert!(!erased_self_ty.has_escaping_bound_vars());
-
-    traits::elaborate_predicates(tcx, predicates)
-        .filter_map(|obligation| {
-            debug!(?obligation);
-            match obligation.predicate.kind().skip_binder() {
-                ty::PredicateKind::Projection(..)
-                | ty::PredicateKind::Trait(..)
-                | ty::PredicateKind::Subtype(..)
-                | ty::PredicateKind::Coerce(..)
-                | ty::PredicateKind::WellFormed(..)
-                | ty::PredicateKind::ObjectSafe(..)
-                | ty::PredicateKind::ClosureKind(..)
-                | ty::PredicateKind::RegionOutlives(..)
-                | ty::PredicateKind::ConstEvaluatable(..)
-                | ty::PredicateKind::ConstEquate(..)
-                | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
-                ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => {
-                    // Search for a bound of the form `erased_self_ty
-                    // : 'a`, but be wary of something like `for<'a>
-                    // erased_self_ty : 'a` (we interpret a
-                    // higher-ranked bound like that as 'static,
-                    // though at present the code in `fulfill.rs`
-                    // considers such bounds to be unsatisfiable, so
-                    // it's kind of a moot point since you could never
-                    // construct such an object, but this seems
-                    // correct even if that code changes).
-                    if t == &erased_self_ty && !r.has_escaping_bound_vars() {
-                        Some(*r)
-                    } else {
-                        None
-                    }
-                }
-            }
-        })
-        .collect()
-}
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index d43b3c9091f..3dfc7a9cacd 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -1,5 +1,4 @@
 use crate::infer::InferCtxt;
-use crate::opaque_types::required_region_bounds;
 use crate::traits;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
@@ -810,3 +809,63 @@ pub fn object_region_bounds<'tcx>(
 
     required_region_bounds(tcx, open_ty, predicates)
 }
+
+/// Given a set of predicates that apply to an object type, returns
+/// the region bounds that the (erased) `Self` type must
+/// outlive. Precisely *because* the `Self` type is erased, the
+/// parameter `erased_self_ty` must be supplied to indicate what type
+/// has been used to represent `Self` in the predicates
+/// themselves. This should really be a unique type; `FreshTy(0)` is a
+/// popular choice.
+///
+/// N.B., in some cases, particularly around higher-ranked bounds,
+/// this function returns a kind of conservative approximation.
+/// That is, all regions returned by this function are definitely
+/// required, but there may be other region bounds that are not
+/// returned, as well as requirements like `for<'a> T: 'a`.
+///
+/// Requires that trait definitions have been processed so that we can
+/// elaborate predicates and walk supertraits.
+#[instrument(skip(tcx, predicates), level = "debug")]
+pub(crate) fn required_region_bounds<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    erased_self_ty: Ty<'tcx>,
+    predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
+) -> Vec<ty::Region<'tcx>> {
+    assert!(!erased_self_ty.has_escaping_bound_vars());
+
+    traits::elaborate_predicates(tcx, predicates)
+        .filter_map(|obligation| {
+            debug!(?obligation);
+            match obligation.predicate.kind().skip_binder() {
+                ty::PredicateKind::Projection(..)
+                | ty::PredicateKind::Trait(..)
+                | ty::PredicateKind::Subtype(..)
+                | ty::PredicateKind::Coerce(..)
+                | ty::PredicateKind::WellFormed(..)
+                | ty::PredicateKind::ObjectSafe(..)
+                | ty::PredicateKind::ClosureKind(..)
+                | ty::PredicateKind::RegionOutlives(..)
+                | ty::PredicateKind::ConstEvaluatable(..)
+                | ty::PredicateKind::ConstEquate(..)
+                | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
+                ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => {
+                    // Search for a bound of the form `erased_self_ty
+                    // : 'a`, but be wary of something like `for<'a>
+                    // erased_self_ty : 'a` (we interpret a
+                    // higher-ranked bound like that as 'static,
+                    // though at present the code in `fulfill.rs`
+                    // considers such bounds to be unsatisfiable, so
+                    // it's kind of a moot point since you could never
+                    // construct such an object, but this seems
+                    // correct even if that code changes).
+                    if t == &erased_self_ty && !r.has_escaping_bound_vars() {
+                        Some(*r)
+                    } else {
+                        None
+                    }
+                }
+            }
+        })
+        .collect()
+}
diff --git a/library/core/src/future/into_future.rs b/library/core/src/future/into_future.rs
index ad9e80e117f..649b4338772 100644
--- a/library/core/src/future/into_future.rs
+++ b/library/core/src/future/into_future.rs
@@ -13,8 +13,6 @@ use crate::future::Future;
 /// on all futures.
 ///
 /// ```no_run
-/// #![feature(into_future)]
-///
 /// use std::future::IntoFuture;
 ///
 /// # async fn foo() {
@@ -33,8 +31,6 @@ use crate::future::Future;
 /// multiple times before being `.await`ed.
 ///
 /// ```rust
-/// #![feature(into_future)]
-///
 /// use std::future::{ready, Ready, IntoFuture};
 ///
 /// /// Eventually multiply two numbers
@@ -91,8 +87,6 @@ use crate::future::Future;
 /// `IntoFuture::into_future` to obtain an instance of `Future`:
 ///
 /// ```rust
-/// #![feature(into_future)]
-///
 /// use std::future::IntoFuture;
 ///
 /// /// Convert the output of a future to a string.
@@ -104,14 +98,14 @@ use crate::future::Future;
 ///     format!("{:?}", fut.await)
 /// }
 /// ```
-#[unstable(feature = "into_future", issue = "67644")]
+#[stable(feature = "into_future", since = "1.64.0")]
 pub trait IntoFuture {
     /// The output that the future will produce on completion.
-    #[unstable(feature = "into_future", issue = "67644")]
+    #[stable(feature = "into_future", since = "1.64.0")]
     type Output;
 
     /// Which kind of future are we turning this into?
-    #[unstable(feature = "into_future", issue = "67644")]
+    #[stable(feature = "into_future", since = "1.64.0")]
     type IntoFuture: Future<Output = Self::Output>;
 
     /// Creates a future from a value.
@@ -121,8 +115,6 @@ pub trait IntoFuture {
     /// Basic usage:
     ///
     /// ```no_run
-    /// #![feature(into_future)]
-    ///
     /// use std::future::IntoFuture;
     ///
     /// # async fn foo() {
@@ -131,12 +123,12 @@ pub trait IntoFuture {
     /// assert_eq!("meow", fut.await);
     /// # }
     /// ```
-    #[unstable(feature = "into_future", issue = "67644")]
+    #[stable(feature = "into_future", since = "1.64.0")]
     #[lang = "into_future"]
     fn into_future(self) -> Self::IntoFuture;
 }
 
-#[unstable(feature = "into_future", issue = "67644")]
+#[stable(feature = "into_future", since = "1.64.0")]
 impl<F: Future> IntoFuture for F {
     type Output = F::Output;
     type IntoFuture = F;
diff --git a/library/core/src/future/mod.rs b/library/core/src/future/mod.rs
index 9b89f766c67..90eecb9d4a0 100644
--- a/library/core/src/future/mod.rs
+++ b/library/core/src/future/mod.rs
@@ -29,7 +29,7 @@ pub use self::future::Future;
 #[unstable(feature = "future_join", issue = "91642")]
 pub use self::join::join;
 
-#[unstable(feature = "into_future", issue = "67644")]
+#[stable(feature = "into_future", since = "1.64.0")]
 pub use into_future::IntoFuture;
 
 #[stable(feature = "future_readiness_fns", since = "1.48.0")]
diff --git a/src/bootstrap/builder.rs b/src/bootstrap/builder.rs
index 2e89abe202c..fa6a5ee1668 100644
--- a/src/bootstrap/builder.rs
+++ b/src/bootstrap/builder.rs
@@ -949,6 +949,7 @@ impl<'a> Builder<'a> {
     }
 
     pub(crate) fn download_component(&self, url: &str, dest_path: &Path, help_on_error: &str) {
+        self.verbose(&format!("download {url}"));
         // Use a temporary file in case we crash while downloading, to avoid a corrupt download in cache/.
         let tempfile = self.tempdir().join(dest_path.file_name().unwrap());
         // While bootstrap itself only supports http and https downloads, downstream forks might
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index e71fbff14dd..ee3b072fe35 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -1558,7 +1558,7 @@ fn download_ci_rustc(builder: &Builder<'_>, commit: &str) {
         builder.fix_bin_or_dylib(&bin_root.join("bin").join("rustc"));
         builder.fix_bin_or_dylib(&bin_root.join("bin").join("rustdoc"));
         let lib_dir = bin_root.join("lib");
-        for lib in t!(fs::read_dir(lib_dir)) {
+        for lib in t!(fs::read_dir(&lib_dir), lib_dir.display().to_string()) {
             let lib = t!(lib);
             if lib.path().extension() == Some(OsStr::new("so")) {
                 builder.fix_bin_or_dylib(&lib.path());
@@ -1634,6 +1634,7 @@ fn download_component(
         }
         Some(sha256)
     } else if tarball.exists() {
+        builder.unpack(&tarball, &bin_root, prefix);
         return;
     } else {
         None
diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index 7ec6eb0be65..272188f8299 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -73,6 +73,8 @@ pub(crate) struct Options {
     pub(crate) proc_macro_crate: bool,
     /// How to format errors and warnings.
     pub(crate) error_format: ErrorOutputType,
+    /// Width of output buffer to truncate errors appropriately.
+    pub(crate) diagnostic_width: Option<usize>,
     /// Library search paths to hand to the compiler.
     pub(crate) libs: Vec<SearchPath>,
     /// Library search paths strings to hand to the compiler.
@@ -331,11 +333,12 @@ impl Options {
         let config::JsonConfig { json_rendered, json_unused_externs, .. } =
             config::parse_json(matches);
         let error_format = config::parse_error_format(matches, color, json_rendered);
+        let diagnostic_width = matches.opt_get("diagnostic-width").unwrap_or_default();
 
         let codegen_options = CodegenOptions::build(matches, error_format);
         let debugging_opts = DebuggingOptions::build(matches, error_format);
 
-        let diag = new_handler(error_format, None, &debugging_opts);
+        let diag = new_handler(error_format, None, diagnostic_width, &debugging_opts);
 
         // check for deprecated options
         check_deprecated_options(matches, &diag);
@@ -699,6 +702,7 @@ impl Options {
             input,
             proc_macro_crate,
             error_format,
+            diagnostic_width,
             libs,
             lib_strs,
             externs,
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 51b245e36ba..8c494ee28cc 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -154,6 +154,7 @@ impl<'tcx> DocContext<'tcx> {
 pub(crate) fn new_handler(
     error_format: ErrorOutputType,
     source_map: Option<Lrc<source_map::SourceMap>>,
+    diagnostic_width: Option<usize>,
     debugging_opts: &DebuggingOptions,
 ) -> rustc_errors::Handler {
     let fallback_bundle =
@@ -169,7 +170,7 @@ pub(crate) fn new_handler(
                     fallback_bundle,
                     short,
                     debugging_opts.teach,
-                    debugging_opts.terminal_width,
+                    diagnostic_width,
                     false,
                 )
                 .ui_testing(debugging_opts.ui_testing),
@@ -187,7 +188,7 @@ pub(crate) fn new_handler(
                     fallback_bundle,
                     pretty,
                     json_rendered,
-                    debugging_opts.terminal_width,
+                    diagnostic_width,
                     false,
                 )
                 .ui_testing(debugging_opts.ui_testing),
@@ -208,6 +209,7 @@ pub(crate) fn create_config(
         crate_name,
         proc_macro_crate,
         error_format,
+        diagnostic_width,
         libs,
         externs,
         mut cfgs,
@@ -266,6 +268,7 @@ pub(crate) fn create_config(
         actually_rustdoc: true,
         debugging_opts,
         error_format,
+        diagnostic_width,
         edition,
         describe_lints,
         crate_name,
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index ded3d9951bd..0d3ec7ecb64 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -462,6 +462,14 @@ fn opts() -> Vec<RustcOptGroup> {
                 "human|json|short",
             )
         }),
+        unstable("diagnostic-width", |o| {
+            o.optopt(
+                "",
+                "diagnostic-width",
+                "Provide width of the output for truncated error messages",
+                "WIDTH",
+            )
+        }),
         stable("json", |o| {
             o.optopt("", "json", "Configure the structure of JSON diagnostics", "CONFIG")
         }),
@@ -733,7 +741,12 @@ fn run_renderer<'tcx, T: formats::FormatRenderer<'tcx>>(
 }
 
 fn main_options(options: config::Options) -> MainResult {
-    let diag = core::new_handler(options.error_format, None, &options.debugging_opts);
+    let diag = core::new_handler(
+        options.error_format,
+        None,
+        options.diagnostic_width,
+        &options.debugging_opts,
+    );
 
     match (options.should_test, options.markdown_input()) {
         (true, true) => return wrap_return(&diag, markdown::test(options)),
diff --git a/src/test/run-make/issue-88756-default-output/output-default.stdout b/src/test/run-make/issue-88756-default-output/output-default.stdout
index 6d16fe5673b..08877af9286 100644
--- a/src/test/run-make/issue-88756-default-output/output-default.stdout
+++ b/src/test/run-make/issue-88756-default-output/output-default.stdout
@@ -110,6 +110,9 @@ Options:
                         never = never colorize output
         --error-format human|json|short
                         How errors and other messages are produced
+        --diagnostic-width WIDTH
+                        Provide width of the output for truncated error
+                        messages
         --json CONFIG   Configure the structure of JSON diagnostics
         --disable-minification 
                         Disable minification applied on JS files
diff --git a/src/test/rustdoc-ui/diagnostic-width.rs b/src/test/rustdoc-ui/diagnostic-width.rs
new file mode 100644
index 00000000000..61961d5ec71
--- /dev/null
+++ b/src/test/rustdoc-ui/diagnostic-width.rs
@@ -0,0 +1,5 @@
+// compile-flags: -Zunstable-options --diagnostic-width=10
+#![deny(rustdoc::bare_urls)]
+
+/// This is a long line that contains a http://link.com
+pub struct Foo; //~^ ERROR
diff --git a/src/test/rustdoc-ui/diagnostic-width.stderr b/src/test/rustdoc-ui/diagnostic-width.stderr
new file mode 100644
index 00000000000..fed049d2b37
--- /dev/null
+++ b/src/test/rustdoc-ui/diagnostic-width.stderr
@@ -0,0 +1,15 @@
+error: this URL is not a hyperlink
+  --> $DIR/diagnostic-width.rs:4:41
+   |
+LL | ... a http://link.com
+   |       ^^^^^^^^^^^^^^^ help: use an automatic link instead: `<http://link.com>`
+   |
+note: the lint level is defined here
+  --> $DIR/diagnostic-width.rs:2:9
+   |
+LL | ...ny(rustdoc::bare_url...
+   |       ^^^^^^^^^^^^^^^^^^
+   = note: bare URLs are not automatically turned into clickable links
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/async-await/await-into-future.rs b/src/test/ui/async-await/await-into-future.rs
index 6e1b155e181..8bf1385b3c5 100644
--- a/src/test/ui/async-await/await-into-future.rs
+++ b/src/test/ui/async-await/await-into-future.rs
@@ -1,8 +1,6 @@
 // run-pass
 // aux-build: issue-72470-lib.rs
 // edition:2021
-#![feature(into_future)]
-
 extern crate issue_72470_lib;
 use std::{future::{Future, IntoFuture}, pin::Pin};
 
diff --git a/src/test/ui/diagnostic-width/flag-human.rs b/src/test/ui/diagnostic-width/flag-human.rs
new file mode 100644
index 00000000000..289bfbabd94
--- /dev/null
+++ b/src/test/ui/diagnostic-width/flag-human.rs
@@ -0,0 +1,9 @@
+// compile-flags: --diagnostic-width=20
+
+// This test checks that `-Z output-width` effects the human error output by restricting it to an
+// arbitrarily low value so that the effect is visible.
+
+fn main() {
+    let _: () = 42;
+    //~^ ERROR mismatched types
+}
diff --git a/src/test/ui/terminal-width/flag-human.stderr b/src/test/ui/diagnostic-width/flag-human.stderr
index 393dcf2b828..393dcf2b828 100644
--- a/src/test/ui/terminal-width/flag-human.stderr
+++ b/src/test/ui/diagnostic-width/flag-human.stderr
diff --git a/src/test/ui/diagnostic-width/flag-json.rs b/src/test/ui/diagnostic-width/flag-json.rs
new file mode 100644
index 00000000000..51a1fb447c7
--- /dev/null
+++ b/src/test/ui/diagnostic-width/flag-json.rs
@@ -0,0 +1,9 @@
+// compile-flags: --diagnostic-width=20 --error-format=json
+
+// This test checks that `-Z output-width` effects the JSON error output by restricting it to an
+// arbitrarily low value so that the effect is visible.
+
+fn main() {
+    let _: () = 42;
+    //~^ ERROR arguments to this function are incorrect
+}
diff --git a/src/test/ui/terminal-width/flag-json.stderr b/src/test/ui/diagnostic-width/flag-json.stderr
index 93c246cb3f5..b21391d1640 100644
--- a/src/test/ui/terminal-width/flag-json.stderr
+++ b/src/test/ui/diagnostic-width/flag-json.stderr
@@ -24,7 +24,7 @@ This error occurs when an expression was used in a place where the compiler
 expected an expression of a different type. It can occur in several cases, the
 most common being when calling a function and passing an argument which has a
 different type than the matching type in the function declaration.
-"},"level":"error","spans":[{"file_name":"$DIR/flag-json.rs","byte_start":244,"byte_end":246,"line_start":7,"line_end":7,"column_start":17,"column_end":19,"is_primary":true,"text":[{"text":"    let _: () = 42;","highlight_start":17,"highlight_end":19}],"label":"expected `()`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/flag-json.rs","byte_start":239,"byte_end":241,"line_start":7,"line_end":7,"column_start":12,"column_end":14,"is_primary":false,"text":[{"text":"    let _: () = 42;","highlight_start":12,"highlight_end":14}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"error[E0308]: mismatched types
+"},"level":"error","spans":[{"file_name":"$DIR/flag-json.rs","byte_start":243,"byte_end":245,"line_start":7,"line_end":7,"column_start":17,"column_end":19,"is_primary":true,"text":[{"text":"    let _: () = 42;","highlight_start":17,"highlight_end":19}],"label":"expected `()`, found integer","suggested_replacement":null,"suggestion_applicability":null,"expansion":null},{"file_name":"$DIR/flag-json.rs","byte_start":238,"byte_end":240,"line_start":7,"line_end":7,"column_start":12,"column_end":14,"is_primary":false,"text":[{"text":"    let _: () = 42;","highlight_start":12,"highlight_end":14}],"label":"expected due to this","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"error[E0308]: mismatched types
   --> $DIR/flag-json.rs:7:17
    |
 LL | ..._: () = 42;
diff --git a/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.rs b/src/test/ui/diagnostic-width/non-1-width-unicode-multiline-label.rs
index 1989ea88635..1989ea88635 100644
--- a/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.rs
+++ b/src/test/ui/diagnostic-width/non-1-width-unicode-multiline-label.rs
diff --git a/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr b/src/test/ui/diagnostic-width/non-1-width-unicode-multiline-label.stderr
index bf277362dba..bf277362dba 100644
--- a/src/test/ui/terminal-width/non-1-width-unicode-multiline-label.stderr
+++ b/src/test/ui/diagnostic-width/non-1-width-unicode-multiline-label.stderr
diff --git a/src/test/ui/terminal-width/non-whitespace-trimming-2.rs b/src/test/ui/diagnostic-width/non-whitespace-trimming-2.rs
index abd9e189a75..abd9e189a75 100644
--- a/src/test/ui/terminal-width/non-whitespace-trimming-2.rs
+++ b/src/test/ui/diagnostic-width/non-whitespace-trimming-2.rs
diff --git a/src/test/ui/terminal-width/non-whitespace-trimming-2.stderr b/src/test/ui/diagnostic-width/non-whitespace-trimming-2.stderr
index 5dbb9ce45ee..5dbb9ce45ee 100644
--- a/src/test/ui/terminal-width/non-whitespace-trimming-2.stderr
+++ b/src/test/ui/diagnostic-width/non-whitespace-trimming-2.stderr
diff --git a/src/test/ui/terminal-width/non-whitespace-trimming-unicode.rs b/src/test/ui/diagnostic-width/non-whitespace-trimming-unicode.rs
index 8d4d1b16279..8d4d1b16279 100644
--- a/src/test/ui/terminal-width/non-whitespace-trimming-unicode.rs
+++ b/src/test/ui/diagnostic-width/non-whitespace-trimming-unicode.rs
diff --git a/src/test/ui/terminal-width/non-whitespace-trimming-unicode.stderr b/src/test/ui/diagnostic-width/non-whitespace-trimming-unicode.stderr
index 1e5ff939832..1e5ff939832 100644
--- a/src/test/ui/terminal-width/non-whitespace-trimming-unicode.stderr
+++ b/src/test/ui/diagnostic-width/non-whitespace-trimming-unicode.stderr
diff --git a/src/test/ui/terminal-width/non-whitespace-trimming.rs b/src/test/ui/diagnostic-width/non-whitespace-trimming.rs
index f6c8d345c65..f6c8d345c65 100644
--- a/src/test/ui/terminal-width/non-whitespace-trimming.rs
+++ b/src/test/ui/diagnostic-width/non-whitespace-trimming.rs
diff --git a/src/test/ui/terminal-width/non-whitespace-trimming.stderr b/src/test/ui/diagnostic-width/non-whitespace-trimming.stderr
index c4ff0e16890..c4ff0e16890 100644
--- a/src/test/ui/terminal-width/non-whitespace-trimming.stderr
+++ b/src/test/ui/diagnostic-width/non-whitespace-trimming.stderr
diff --git a/src/test/ui/terminal-width/tabs-trimming.rs b/src/test/ui/diagnostic-width/tabs-trimming.rs
index ade21753b45..ade21753b45 100644
--- a/src/test/ui/terminal-width/tabs-trimming.rs
+++ b/src/test/ui/diagnostic-width/tabs-trimming.rs
diff --git a/src/test/ui/terminal-width/tabs-trimming.stderr b/src/test/ui/diagnostic-width/tabs-trimming.stderr
index 6c8d9afc73b..6c8d9afc73b 100644
--- a/src/test/ui/terminal-width/tabs-trimming.stderr
+++ b/src/test/ui/diagnostic-width/tabs-trimming.stderr
diff --git a/src/test/ui/terminal-width/whitespace-trimming-2.rs b/src/test/ui/diagnostic-width/whitespace-trimming-2.rs
index c68f678aab3..c68f678aab3 100644
--- a/src/test/ui/terminal-width/whitespace-trimming-2.rs
+++ b/src/test/ui/diagnostic-width/whitespace-trimming-2.rs
diff --git a/src/test/ui/terminal-width/whitespace-trimming-2.stderr b/src/test/ui/diagnostic-width/whitespace-trimming-2.stderr
index 97a64e603b7..97a64e603b7 100644
--- a/src/test/ui/terminal-width/whitespace-trimming-2.stderr
+++ b/src/test/ui/diagnostic-width/whitespace-trimming-2.stderr
diff --git a/src/test/ui/terminal-width/whitespace-trimming.rs b/src/test/ui/diagnostic-width/whitespace-trimming.rs
index f747bcf17e0..f747bcf17e0 100644
--- a/src/test/ui/terminal-width/whitespace-trimming.rs
+++ b/src/test/ui/diagnostic-width/whitespace-trimming.rs
diff --git a/src/test/ui/terminal-width/whitespace-trimming.stderr b/src/test/ui/diagnostic-width/whitespace-trimming.stderr
index e296d48893c..e296d48893c 100644
--- a/src/test/ui/terminal-width/whitespace-trimming.stderr
+++ b/src/test/ui/diagnostic-width/whitespace-trimming.stderr
diff --git a/src/test/ui/terminal-width/flag-human.rs b/src/test/ui/terminal-width/flag-human.rs
deleted file mode 100644
index e445a84fd01..00000000000
--- a/src/test/ui/terminal-width/flag-human.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-// compile-flags: -Z terminal-width=20
-
-// This test checks that `-Z terminal-width` effects the human error output by restricting it to an
-// arbitrarily low value so that the effect is visible.
-
-fn main() {
-    let _: () = 42;
-    //~^ ERROR mismatched types
-}
diff --git a/src/test/ui/terminal-width/flag-json.rs b/src/test/ui/terminal-width/flag-json.rs
deleted file mode 100644
index 3d2530e204b..00000000000
--- a/src/test/ui/terminal-width/flag-json.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-// compile-flags: -Z terminal-width=20 --error-format=json
-
-// This test checks that `-Z terminal-width` effects the JSON error output by restricting it to an
-// arbitrarily low value so that the effect is visible.
-
-fn main() {
-    let _: () = 42;
-    //~^ ERROR arguments to this function are incorrect
-}
diff --git a/src/tools/clippy/clippy_lints/src/misc.rs b/src/tools/clippy/clippy_lints/src/misc.rs
index df2430ced6b..be7df08d89f 100644
--- a/src/tools/clippy/clippy_lints/src/misc.rs
+++ b/src/tools/clippy/clippy_lints/src/misc.rs
@@ -301,7 +301,7 @@ fn in_attributes_expansion(expr: &Expr<'_>) -> bool {
     use rustc_span::hygiene::MacroKind;
     if expr.span.from_expansion() {
         let data = expr.span.ctxt().outer_expn_data();
-        matches!(data.kind, ExpnKind::Macro(MacroKind::Attr, _))
+        matches!(data.kind, ExpnKind::Macro(MacroKind::Attr|MacroKind::Derive, _))
     } else {
         false
     }
diff --git a/src/tools/clippy/tests/ui/used_underscore_binding.rs b/src/tools/clippy/tests/ui/used_underscore_binding.rs
index 21d66d5df79..d20977d55d2 100644
--- a/src/tools/clippy/tests/ui/used_underscore_binding.rs
+++ b/src/tools/clippy/tests/ui/used_underscore_binding.rs
@@ -44,6 +44,12 @@ fn in_struct_field() {
     s._underscore_field += 1;
 }
 
+/// Tests that we do not lint if the struct field is used in code created with derive.
+#[derive(Clone, Debug)]
+pub struct UnderscoreInStruct {
+    _foo: u32,
+}
+
 /// Tests that we do not lint if the underscore is not a prefix
 fn non_prefix_underscore(some_foo: u32) -> u32 {
     some_foo + 1
diff --git a/src/tools/clippy/tests/ui/used_underscore_binding.stderr b/src/tools/clippy/tests/ui/used_underscore_binding.stderr
index 790b849210c..61a9161d212 100644
--- a/src/tools/clippy/tests/ui/used_underscore_binding.stderr
+++ b/src/tools/clippy/tests/ui/used_underscore_binding.stderr
@@ -31,7 +31,7 @@ LL |     s._underscore_field += 1;
    |     ^^^^^^^^^^^^^^^^^^^
 
 error: used binding `_i` which is prefixed with an underscore. A leading underscore signals that a binding will not be used
-  --> $DIR/used_underscore_binding.rs:99:16
+  --> $DIR/used_underscore_binding.rs:105:16
    |
 LL |         uses_i(_i);
    |                ^^